It is important for photopolymer compositions utilized in making printing plates to have a high degree of clarity so that ultra-violet light which is transmitted through a photographic negative can penetrate the composition and initiate cure. It is also critical for the photopolymer composition to exhibit a high degree of water swell which allows for easy scrub-off of that part of the printing plate which was not cured. There are also certain mechanical requirements needed from such photopolymer compositions.
U.S. Pat. No. 4,045,231 discloses the utilization of polystyrene-polybutadiene-polystyrene triblock polymers in printing plates. U.S. Pat. No. 4,162,919 discloses the employment of styrene-isoprene diblock polymers and styrene-isoprene diblock polymers in flexographic printing plates. U.S. Pat. No. 5,344,743 discloses flexographic photosensitive printing plates which are made with formulations comprising triblock polymers of poly(vinylpyridine)-poly(butadiene) or poly(isoprene)-poly(vinylpyridine).
Certain carboxylated nitrile rubbers, such as Chemigum.RTM. NX775 carboxylated nitrile rubber which is sold by The Goodyear Tire & Rubber Company, offer most of the physical requirements needed from a base polymer for printing plate photopolymer compositions. However, such carboxylated nitrile rubbers do not have adequate clarity and are too water resistant for utilization in such applications. It is also important for carboxylated nitrile rubbers utilized in such applications to have a Mooney ML-4 viscosity of less than about 80.
U.S. Pat. No. 4,415,690, U.S. Pat. No. 4,435,535, and U.S. Pat. No. 4,452,936 disclose techniques for preparing carboxylated nitrile rubbers which are suitable for utilization in making printing plate photopolymer compositions but for their inadequate clarity and water swell characteristics. U.S. Pat. No. 4,415,690 discloses the utilization of succinic anhydride derivatives as scorch inhibiting agents. U.S. Pat. No. 4,435,535 discloses the utilization of adipic acid as a scorch inhibiting agent, and U.S. Pat. No. 4,452,936 discloses the utilization of oligomerized fatty acids as scorch inhibiting agents.